Well now I've done it.
I had a bunch of LEDs show up today, Yay!
So first I went through and replaced all the general illumination bulbs. I discovered one bad socket, but all the rest worked - and the better illumination is really nice.
But it also revealed just how weak the incandecents were - so the next LED to go in was in the center thumper bumper. That worked great.
I have 2 red and one orange - the reds went into the "holes score 2000" lights, and the orange went into "same player shoot again". Then I did all the playfield lights for the player 1 holes.
Power up the machine, and man alive do those inserts look better with LEDs in them - and they all powered up too!
So far, so good.
So I put the glass back on, started a game... and now getting a ball into a pocket does not power off the associated light nor light the light in the backglass. It *does* score the points (so it runs the score motor) and it *does* eject the ball, but you cannot progress to the 8 ball.
So, into the manual to look at relay pinouts, playfield up and power on to try triggering things and see what happens.
In the manual, there are 2 big relay banks - one drives the player 1 ball lights, the other drives the player 2 ball lights. These relays are mechanically latched, like a suitcase latch. At startup, a big bar comes down and resets all the relays to "locked". When an individual relay fires, it "unlatches" and turns off the playfield light and turns on the backglass light. It also closes a switch in series to all the other player ball lights and the 8 ball, so when all the balls have been unlatched, the 8 ball light comes on so it can be hit for the extra ball and the change of score to 2000 points per hit instead of 500.
If I manually unlatch a relay, it flips the lights as expected. If I unlatch all the relays in the bank, the 8 ball lights. Trigger the 8 ball, and the extra ball lights and the "holes score 2000" lights come on (LEDs nice and bright). Trigger any hole, and it score 2000pts like it should. Sink the ball, and it unlatches the 2000pt lights and scoring, and a big reset bar comes down and mechanically re-locks all the ball relays, and the playfield lights come on and backglass lights go out - so all the logic behind the hole relay banks is working fine. All that is missing is the electric de-latching of individual balls.
Each ball hole has a little plunger with 2 leaf switches on it. 1 leaf switch runs the score motor and awards points. The other appears to fire the ball coil unlocking relay. Aha!
Now here is where it gets weird.
There are 2 holes on the playfield that have 2 balls associated with them, meaning you have to hit the hole twice to clear the hole on the way to the 8 ball shot. These lights always go in sequence, meaning that if the hole has the 1 and the 5 relay associated with it, the 1 will always clear first, then the 5.
If I manually unlock the first relay associated with that hole, tripping that hole a second time *will electrically unlock the second relay associated with that hole and flip the lights*
So a single light hole or the first light of a double-light hole does not respond to its energizing switch, but the second light of a double-light hole *does*.
There are also a pair of relays - one called the "1-7" relay, the other the "9-15" relay - that are responsible for shifting to which bank of ball relays is in play depending on if Player 1 (Solids) or player 2 (Stripes) is up. Those relays are under the playfield, so it is possible I bumped one of them trying to get the insert LED bulbs in. But they both appear to be working, in that the lighting for the inserts switches correctly when the player up changes, and they are wired basically "1 switch per hole" so it is incredibly unlikely I'd knock them *all* out of adjustment. It seems much more likely that I somehow interrupted power to the relay energization switch in each hole somehow.
I really really wish I had the wiring diagram right now.